Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$92.83	10.625%	$102.6932	$102.69	$102.70	$102.70
Purchase #2	$136.83	11.284%	$152.2699	$152.27	$152.25	$152.30
Purchase #3	$111.31	8.451%	$120.7168	$120.72	$120.70	$120.70
Purchase #4	$41.71	9.441%	$45.6478	$45.65	$45.65	$45.60
Purchase #5	$76.49	8.488%	$82.9825	$82.98	$83.00	$83.00
Purchase #6	$170.32	3.515%	$176.3067	$176.31	$176.30	$176.30
Purchase #7	$96.65	12.842%	$109.0618	$109.06	$109.05	$109.10
7 purchase totals =	$726.14		$789.6787	$789.68	$789.65	$789.70